---
title: "List customers in a segment"
method: GET
path: "/v1/segments/{segment_id}/membership"
tags: ["Segments"]
---

# List customers in a segment

`GET /v1/segments/{segment_id}/membership`

Returns customers in a segment. This endpoint returns an array of `identifiers`; each object in the array represents a person and contains the identifier values allowed in your workspace. In general, we recommend that you use `identifiers` rather than `ids` to find people, because it provides more information.

**If your workspace does not use email as a unique identifier** for people, `identifiers` does not contain `email` values. Go to your [Workspace Settings](/accounts/workspaces#migrate-workspace) to find out which identifiers your workspace supports.

The `ids` array only lists ID values for people in a segment; if your workspace uses both `email` and `id` as identifiers, it's possible that a member of your segment does not have an `id` value, resulting in an empty string in the `ids` array.

## Response `200`

Returns an array of customers for a segment.

- union
  - object
    - `segment_id` integer — The identifier for a segment; used to target a segment in requests.
    - `ids` string[] — The customers that belong to this segment.
    - `identifiers` CustomerIdentifiers[] — The customers that belong to this segment.
      - `email` string, email, nullable, required — A person's email address, if set.
      - `id` string, nullable, required — A person's unique ID, if set. This is the same as the `customer_id` if present.
      - `cio_id` string, required — A unique identifier set by Customer.io, used to reference a person if you want to update their identifiers.
    - `next` string — Indicates the next page of results. Add `?start=<next_value>` to the request to get the next page of results.
  - object
    - `segment_id` integer — The identifier for a segment; used to target a segment in requests.
    - `ids` string[] — The customers that belong to this segment.
    - `identifiers` object[] — The customers that belong to this segment.
      - `id` string, required — A person's unique ID. This matches a value in `ids`.
      - `cio_id` string, required — A unique identifier set by Customer.io, used to reference a person if you want to update their identifiers.
    - `next` string — Indicates the next page of results. Add `?start=<next_value>` to the request to get the next page of results.

## Other responses

- `404` — The `segment_id` does not exist.
- `429` — Your request is over the 10-per-second limit. `Retry-After` tells you how many seconds you must wait before you send the next request.

## Changes

- **2026-09-02** `5da2740beeb5` — 1 info
  - added the media type `application/json` for the response with the status `429`

[Change history](https://skmtc.dev/customer/apis/customer-io-journeys-api-reference/changes/v1/segments/:segment_id/membership/get.md)

---

[API](https://skmtc.dev/customer/apis/customer-io-journeys-api-reference.md) · [All operations](https://skmtc.dev/customer/apis/customer-io-journeys-api-reference/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/customer/customer-io-journeys-api-reference/revisions/5da2740beeb5/schema)